Organic light emitting diode

Abstract

This disclosure generally relates to improved structures for organic light emitting diodes (OLEDs), and more particularly to so-called top emitting OLEDs.

1. An organic light emitting diode (OLED) comprising a substrate bearing a light emitting layer between an electrically conducting anode and an electrically conducting cathode, the diode being configured for light emission through said cathode, the cathode being transmissive at a light emission wavelength of the diode, the cathode comprising an electron injecting layer for injecting electrons into said light emitting layer, an optical interference structure, and an electrically conducting layer, said electron injecting layer being closest to the light emitting layer and said optical interference structure being disposed between said electron injecting and electrically conducting layers, wherein said optical interference structure is configured to enhance light transmission through said cathode at said emission wavelength and comprises an optical interference layer disposed between first and third layers of different refractive indices such that reflections from front and back surfaces of said optical interference layer interfere to enhance light transmission through said cathode at said emission wavelength, said first layer comprising the electron injecting layer for injecting electrons into said light emitting layer, said third layer comprising the electrically conducting layer, and said optical interference layer having an optical thickness of between a third of said emission wavelength and a fifth of said emission wavelength. 
     
     
       2. An OLED as claimed in  claim 1  wherein said optical interference layer has an optical thickness of substantially a quarter of said emission wavelength. 
     
     
       3. An OLED as claimed in  claim 1  wherein said emission wavelength is substantially equal to a peak or center emission wavelength of said light emitting layer. 
     
     
       4. An OLED as claimed in  claim 1  wherein said third layer comprises a metal layer. 
     
     
       5. An OLED as claimed in  claim 1  wherein said optical interference layer comprises a wide bandgap semiconductor. 
     
     
       6. An OLED as claimed in  claim 1  wherein said optical interference layer comprises a transparent conductor. 
     
     
       7. An OLED as claimed in  claim 1  wherein said optical interference layer comprises a dielectric material. 
     
     
       8. An OLED as claimed in  claim 1  wherein said electron injecting layer includes a layer of a metal. 
     
     
       9. A display device including an OLED as claimed in  claim 1 . 
     
     
       10. An organic light emitting diode (OLED)-based display device including one or more OLEDs each comprising a layer of OLED material sandwiched between anode and cathode electrode layers, said OLED material electroluminescing when a current is passed between said anode and cathode electrode layers, a first of said electrode layers being at least partially transmissive at a peak wavelength of said electroluminescence and being closer to a display surface of said device than the second of said electrode layers whereby the device is configured for electroluminescent display through said first electrode layer, wherein said first electrode layer comprises a spacer layer sandwiched between a coupling layer for connecting to said OLED material and a third, substantially electrically conductive layer, said coupling layer and said substantially electrically conductive layer having different refractive indices such that reflections from front and back surfaces of said spacer layer interfere to enhance light transmission through said cathode at said emission wavelength and wherein said spacer layer has a thickness of approximately an odd integral number of quarter wavelengths at said peak electroluminescence wavelength such that transmission through said first electrode layer at said peak electroluminescence wavelength is substantially maximized. 
     
     
       11. An OLED-based display device as claimed in  claim 10  wherein said first electrode layer is said cathode electrode layer. 
     
     
       12. An OLED as claimed in  claim 5  wherein said wide bandgap semiconductor comprises zinc selenide or gallium nitride. 
     
     
       13. An OLED as claimed in  claim 6  wherein said transparent conductor comprises indium tin oxide or indium zinc oxide.